Digital images are currently used in many applications, for example in new generation acquisition devices, such as digital cameras or DSC (Digital Still Camera). Moreover, digital images are becoming more widely used in portable multimedia communication terminals.
Typically, a digital image is represented by a pixel matrix. The total number of pixels present in said matrix defines the spatial resolution of the image. Each pixel is identified by a pair of spatial coordinates that correspond to the position of the pixel inside the matrix and by one or more digital values associated to it, each of which represents a parameter of the pixel. For example, three digital values are associated to each pixel in an RGB format color digital image, representative of the following parameters respectively: intensity of the red color component, intensity of the green color component and intensity of the blue color component.
In numerous applications, representation of a digital image as a pixel matrix is not optimal because it requires a large quantity of memory and it cannot be enlarged at will without this leading to a considerable loss in quality.
It is known that a digital image can be stored and processed with a method known in the art as vector representation or format. A method that uses this format provides for the image to be represented as a plurality of regions that are not superimposed but altogether cover the entire image. The information necessary to define the contours of said regions are stored, while the information regarding the pixel parameters comprised in each region are summarized in a few parameters generically associated to the entire region or only associated with a limited number of pixels in the region. It can be seen from the above that transformation of a digital image originally represented by means of a pixel matrix to a corresponding image represented by means of the above-described vector format method leads to a reduction in the quantity of information necessary to describe the image and, therefore, to a greater image transmission speed and a lower memory requirement for its storage.
It is known, furthermore, that in particular applications, such as zooming techniques and processing techniques in general that require an increase/decrease (i.e. resizing) in the spatial resolution of the image, vector representation is more convenient and efficient than pixel matrix representation.
It has been observed that numerous raster-to-vector conversion methods belonging to the state of the art, even if widely used, do not guarantee satisfactory performance in terms of the dimensions occupied by the vectorized images and in terms of the measured or perceived quality of said images.